Pre-hospital care is the critical first step in acute stroke management, but is currently constrained by deficiencies in dispatcher and paramedic recognition and characterization of stroke in the field. The general aim of this Project is to devise, implement, and validate novel strategies for rapid assessment, triage, and treatment of acute stroke in the field. This aim will be achieved by conducting three studies. In Study 1, "Characterizing Stroke Severity in the Field," the primary aim is to validate a novel instrument to characterize stroke severity in the field for use by prehospital personnel. This aim will be achieved by performing a prospective, in the field validation trial of the Los Angeles Motor Scale (LAMS) in consecutively encountered acute potential stroke patients to demonstrate criterion validity, predictive validity, physiologic validity, and discriminant validity. In Study 2, "Improving Stroke Recognition by EMS Dispatchers," the primary aim is to improve identification of stroke patients by Emergency Medical Services dispatch personnel. This aim will be achieved by constructing a version of the Los Angeles Pre-hospital Stroke Screen modified for dispatch use (LAPSS-Dispatch), and then conducting a prospective validation trial to determine its sensitivity, specificity, positive predictive value, negative predictive value, and overall accuracy. In Study 3, "Prehospital Diagnosis of Stroke by Biomarker Testing, Feasibility, Validation and Impact Studies, the primary aim is to improve prehospital identification of stroke by use of a point of care diagnostic test that assays five blood biomarkers to distinguish true stroke from stroke mimics. This aim will be achieved by performing two studies in succession: a) A prospective, in the field study in consecutively encountered acute potential stroke patients to determine the feasibility and sensitivity, specificity, positive predictive value, negative predictive value, and overall accuracy of paramedic-performed point of care diagnostic biomarker testing for stroke; b) a successor prospective, in the field of study in consecutively encountered acute potential stroke patients to assess the impact of incorporating into treatment decision-making results of paramedic-performed point of care diagnostic bio-marker testing for stroke.